About this scene
She's at the end of the aisle when she clocks it. The sunglasses don't come off. They come down. She tilts her chin a quarter inch, drops the frames to the bridge of her nose, and looks straight over the top. Whatever she was reaching for on the shelf goes back without her remembering she'd picked it up. The whole moment is maybe twenty seconds long. She doesn't smile, doesn't move closer, doesn't do anything you'd notice from across the store. Her shopping cart stays put. Her stare doesn't.
What to watch for
The sunglasses move is the whole video. Watch her right hand. It comes up halfway, like she's about to lift the frames off completely, then thinks better of it and just nudges them lower. That's a deliberate choice. Lifting them off would mean openly staring. Lowering them keeps deniability if anyone walks past. She stays in that exact pose for the rest of the clip. Nothing else needs to happen.